Performance of an engine can be enhanced via a turbocharger or a supercharger. The turbocharger or supercharger pressurizes ambient air to increase the density of air entering engine cylinders. The cylinder trapped air amount is increased as the cylinder charge may be denser than that of a non-turbocharged engine. This may allow increased amount of fuel injected to be into the engine cylinder compared to a non-turbocharged engine, hence result in increased torque.
Further performance gains and emissions reduction may be provided for a turbocharged engine via variable intake and/or exhaust valve timing. In particular, intake and exhaust valves of a turbocharged engine may be adjusted to reduce NOx formation, increase engine power, and reduce engine pumping losses. In some examples, intake and exhaust valves of a cylinder may be open at the same time to provide internal (e.g., within a cylinder) exhaust gas recirculation (EGR) or to help evacuate exhaust from a cylinder and increase engine output.
For example, internal EGR may be provided in an engine cylinder when intake and exhaust valves are simultaneously open and when engine intake manifold pressure is lower than engine exhaust manifold pressure. On the other hand, engine output power may be increased when intake and exhaust valves of a cylinder are simultaneously open and when engine intake manifold pressure is higher than engine exhaust manifold pressure. Pressurized air in the engine intake manifold can drive exhaust gases from the cylinder to the engine exhaust manifold so that cylinder fresh charge (e.g. air and fuel) may be increased. However, if engine control parameters (e.g., spark timing) are adjusted based on an uncorrected air amount or a bulk air amount that passes through a cylinder, the engine control parameters may be adjusted in an undesirable way. Further, the output of modeled systems (e.g., exhaust systems) that rely on cylinder trapped air amount may not track actual system conditions as close as is desired because of errors that may result from the uncorrected cylinder trapped air amount or the bulk air amount.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: adjusting a first actuator in response to an cylinder scavenging air amount, the cylinder scavenging air amount corrected via an oxygen sensor; and adjusting a second actuator in response to a cylinder trapped air amount, the cylinder trapped air amount corrected via the oxygen sensor apart from the cylinder scavenging air amount.
By correcting both cylinder trapped air amount and cylinder scavenging air amount via an oxygen sensor, it may be possible to improve control adjustments that are related to total cylinder air flow. Additionally, conditions that may affect cylinder trapped air amount but may not be sensed via a mass air sensor or MAP sensor may be compensated when cylinder trapped air amount and cylinder scavenging are adjusted via an oxygen sensor. For example, rather than adjusting spark timing based on a total or bulk air mass passing through a cylinder during a cylinder cycle, spark timing may be adjusted based on a corrected cylinder trapped air amount that reflects the amount of air participating in combustion. Further, intake and exhaust valve opening overlap of a cylinder may be adjusted in response to a corrected cylinder scavenging air amount. In this way, fractions or portions of an air amount flowing through a cylinder during a cylinder cycle that participate in combustion during a cylinder cycle can be corrected and compensated for separately. In addition, correcting cylinder trapped air amount and cylinder scavenging air amount via an oxygen sensor can remove sensitivities to changes in exhaust system manifold pressure and valve timing that may exist when cylinder trapped air amount and cylinder scavenging air amount are determined solely using a mass air flow sensor or a MAP sensor.
The present description may provide several advantages. In particular, the approach may reduce vehicle emissions by correcting cylinder trapped air amount and cylinder scavenging air amounts. Further, an engine actuator such as a camshaft phase actuator may be adjusted so as to control the amount of scavenging supplied to the exhaust gas after treatment device so that scavenging may closed-loop controlled. Additionally, the method provides for adjusting exhaust manifold pressure estimates so that exhaust gas residuals in a cylinder may be more accurately determined.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.